This invention relates to near-field RF communicators and near-field communications enabled devices and to their methods of operation.
Near-field RF (radio frequency) communication is becoming more and more commonplace as is the use of such technology to transfer data. Near-field RF communicators communicate through the modulation of the magnetic field (H field) generated by a radio frequency antenna. Near-field RF communication thus requires an antenna of one near-field RF communicator to be present within the alternating magnetic field (H field) generated by the antenna of another near-field RF communicator by transmission of an RF signal (for example a 13.56 MHz signal) to enable the magnetic field (H field) of the RF signal to be inductively coupled between the communicators. The RF signal may be modulated to enable communication of control and/or other data. Ranges of up to several centimetres (generally a maximum of 1 meter) are common for near-field RF communicators.
NFC communicators are a type of near-field RF communicator that is capable in an initiator mode of initiating a near-field RF communication (through transmission or generation of an alternating magnetic field) with another near-field RF communicator and is capable in a target mode of responding to initiation of a near-field RF communication by another near-field RF communicator. The term “near-field RF communicator” includes not only NFC communicators but also initiator near-field RF communicators such as RFID transceivers or readers that are capable of initiating a near-field RF communication but not responding to initiation of a near-field RF communication by another near-field RF communicator and target or responding near-field RF communicators such as RFID transponders or tags that are capable of responding to initiation of a near-field RF communication by another near-field RF communicator but not of initiating a near-field RF communication with another near-field RF communicator. Hence NFC communicators can act as both RFID transceivers and RFID transponders and are able to communicate with other NFC communicators, RFID transceivers and RFID transponders.
In addition NFC communicators may be associated with or comprised within or attached to certain peripheral devices, for example SIM cards (e.g. UICC), Secure Elements, memory devices (for example MCU, RAM, ROM and non-volatile memory), display driver or other drivers. During operation the NFC communicator must also be able to communicate with and transfer data to and from such peripheral devices.
There are several standards in existence which set out certain communication protocols and functional requirements for RFID and near-field RF communications. Examples are ISO/IEC 14443, ISO 15693, ISO/IEC 18092 and ISO/IEC 21481.
NFC and Near-field RF communicators may be comprised within a larger device, such as a mobile telephone, PDA or computer which may comprise a high frequency (e.g. VHF, “FM” or UHF) receiver and transmitter for long range communications for example using GSM or Wi-Fi frequencies. When a near-field RF communicator is comprised within such host devices it is advantageous to reduce emissions from the NFC communicator in frequency bands employed by the host device.
A near-field RF communicator operating in an initiator mode, such as an NFC communicator or other initiator near-field RF communicators, for example an RFID transceiver or reader that is capable of initiating a near-field RF communication, employs a polling sequence to detect whether another near-field RF communicator is present in near-field range and, if so, the communications protocol used by the other near-field RF communicator.
In a typical polling sequence the near-field RF communicator operating in an initiator mode switches on, and generates a carrier signal. After waiting sufficient time for the carrier signal to settle down, the communicator transmits a series of hand shake or “wake-up” signals. Each wake-up signal is configured to initiate communication with a different type of near-field RF communicator, such as different types of RFID tags. A typical polling sequence includes, for example, a wake-up signal for a type-1 tag, a wake-up signal for a type-2 tag and then a wake-up signal for a type-3 tag. Such polling sequences are described in RFID and near-field RF communications standards.
Where a polling sequence includes a separate “wake-up” signal for each of several types of near-field RF communicator, the total duration of each cycle of the polling sequence can be significant. For example a polling sequence according to an accepted near-field communications standard may exceed 10 ms and may be as much as 50 ms or 100 ms. Where the power source of a near-field RF communicator operating in initiator mode is derived from a battery powered host device, the energy required repeatedly to perform a polling sequence may significantly reduce the battery life of that host device.
To preserve battery life it has been proposed to reduce the frequency with which a polling sequence is performed. However, this reduces the perceived responsiveness of the near-field communicators because there may be a delay before communication is initiated after two near-field RF communicators are brought into reading range of each other. In other words, a user's perception of the responsiveness of devices comprising near-field RF communicators is dependent on the time taken to initiate communication. Thus, in order for a near-field RF communicator to respond quickly to the presence of a passive near-field RF communicator (or a near-field RF communicator operating in target mode) coming in to near-field range it has been proposed to perform the polling sequence at frequent intervals. This requires greater energy and may not be desirable in battery operated devices.
Thus there exists a need in the art for a near-field RF communicator which responds quickly to a passive (or target mode) near-field RF communicator coming into near-field range whilst also providing improved power management characteristics.